How to create an image with transparency
It depends on what you are actually asking:


If you need ot create an RGBA image, so an image that also has the Alpha Channel. (So a RGBA type instead of the normal RGB). Just Check ALPHA when you create it via UI or in code:

bpy.data.images.new("albedo", width=1024, height=1024, alpha = True)
If you want the default color to be instead of black any other color so even one with some transparency, this is the fastest way I found: 


im = bpy.data.images.new("albedo", width=1024, height=1024, alpha = True)
im.generated_color = (1,0,0,0.5)


This code actually generates a Red image half transparent.